Apparatus for converting a pump to a controller

ABSTRACT

Apparatus is provided for assuring that fluid is introduced from a pump to a receiver, such as a patient, at a controlled and safe pressure. This arrangement includes conduit means, such as inlet and outlet lines, which extend from the pump to the receiver and which are included in a disposable unit. The disposable unit includes detent means cooperative with detent means in the pump to hold the disposable unit in releasable relationship with the pump. 
     Resilient means such as diaphragm are disposed in the conduit means in the disposable unit. The resilient means expand or contract in accordance with the pressure of the fluid in the outlet line. Actuatable means such as an actuatable arm is disposed in the disposable unit and is captured in the conduit means and is positioned in abutting relationship with the diaphragm for movement with the diaphragm. 
     When the pressure of the fluid in the output line reaches a particular value, the actuating arm becomes displaced through a particular distance to operate sensing means external to the disposable unit. The operation of the sensing means causes an output indicator to be energized. 
     The particular pressure for operating the sensing means is dependent upon the adjustable positioning of control means, such as a knob, external to the disposable unit. The manual adjustment of the knob causes a control member to be adjusted in position. The adjustment in the position of the control member may produce a corresponding adjustment in the force required to actuate the arm, thereby producing an adjustment in the fluid pressure at which the sensing means becomes operative.

This invention relates to apparatus for use with a pump for controllingthe pressure introduced from the pump to a receiver such as a patient.More particularly, the invention relates to apparatus for controllingthe pressure of the fluid introduced from a pump to a receiver such as apatient to assure that the pressure of the fluid introduced to thepatient is within selected limits.

Various instrumentalities have been provided in recent years forintroducing fluid to a patient. For example, various pumps have beenprovided for pumping fluid to a patient at a particular rate on apositive basis. For example, U.S. Pat. No. 3,985,133 issued to me, ORRISH. FLATTEN and OSCAR E. HYMAN as joint inventors and assigned of recordto the assignee of record of this application discloses and claims avolumetric pump which introduces a controlled amount of fluid at apre-selected rate to a patient.

Although pumps are advantageous in that they introduce fluid to apatient on a positive basis, pumps occasionally offer difficulties inthat they may introduce the fluid to the patient at pressures greaterthan the pressures which would ordinarily be considered desirable. Thisis particularly true when fluids are introduced to infants or theelderly.

Controllers have also been provided for introducing fluid to a patienton a gravitational basis. Such controllers have been advantageous inthat they operate at the relatively low pressures which are indicatedfor infants and the elderly. However, controllers have beendisadvantageous until now in that they have not provided for the flow ofcontrolled amounts of fluid at pre-selected rates to a patient by apositive displacement of fluid.

Until now, no one has provided an instrument with the advantages of botha pump and a controller. Specifically, no one has provided a unit whichintroduces a controlled amount of fluid to a patient at a low andpre-selected pressure and at a pre-selected rate by a positivedisplacement of such fluid. No one has specifically provided apparatuswhich is able to operate with any type of pump to provide suchadvantages. Considerable efforts have been devoted to providing such aunit but such efforts have not been entirely fruitful.

This invention provides a unit with the advantages of both a pump and acontroller. The invention provides the advantages of a pump--actually,any kind of pump--by producing a flow of fluid at a controlled rate by apositive displacement of such fluid. The invention provides the furtheradvantages of a controller by producing the flow of fluid at the lowpressures which are indicated even for infants and the elderly.

The invention is also advantageous in providing a disposable cassettewhich is releasably coupled to a pump to convert the operation of thepump into the operation of a controller. The cassette is advantageous inthat all of the fluid flows through the disposable cassette. In thisway, each individual cassette can be used for a different patient andcan then be removed from the pump and can be replaced by a new cassettewhen a different patient is treated or a different treatment is appliedto the same patient.

In one embodiment of the invention, a disposable cassette is providedwith a housing having detent means for a releasable engagement withdetent means on a pump. The cassette includes conduit means defininginlet and outlet lines and a chamber between the lines. The inlet linereceives fluid from the pump and the outlet line passes the fluid to apatient. Resilient means such as a diaphragm are disposed at aparticular position in the chamber and are extendable in accordance withthe pressure of the fluid in the chamber. An activating arm is capturedin the cassette for movement in accordance with the extension of thediaphragm.

The activating arm may produce the operation of a sensor when theactuating arm has moved through a particular distance. The sensor may beincluded in a unit forming a part of the pump or it may be provided as aseparate unit. When the unit forms a part of the pump, the actuating armin the cassette may extend a resilient diaphragm on the face of the pumpin accordance with the movements of the arm. This resilient diaphragmmay in turn actuate a flag in accordance with the extension of thediaphragm. When the flag has been moved through a particular distance,it causes the sensor to be energized. The particular pressure necessaryto move the flag through the particular distance may be adjusted bymanually adjusting a knob. In this way, the adjustment of the knobcontrols the fluid pressure at which the sensor becomes energized.

In the drawings:

FIG. 1 is a sectional view, partially schematic, of a pump and of oneembodiment of apparatus constituting this invention for operating withthe pump to control the pressure of fluid from the pump;

FIG. 2 is a sectional view similar to that shown in FIG. 1 but with theapparatus in position for discontinuing the operation of the pump;

FIG. 3 is an enlarged fragmentary elevational view of sensors includedin the apparatus of FIGS. 1 and 2;

FIG. 4 is a sectional view, partially schematic, of another embodimentof apparatus constituting this operation for operating with a pump tocontrol the pressure of fluid from the pump; and

FIG. 5 is a perspective view of the embodiment shown in FIG. 4.

In the embodiment of the invention shown in FIGS. 1 through 3, a pumpgenerally indicated at 10 is provided for pumping fluid at a controlledrate to a patient 14 on a positive basis. The pump 10 may be avolumetric pump such as disclosed and claimed in U.S. Pat. No.3,985,133. Such a pump is advantageous because it provides a flow of apre-selected volume of fluid at a precise rate to a patient. However,any other type of pump may also be used.

U.S. Pat. No. 3,985,133 also discloses a disposable cassette for usewith the pump. FIG. 1 shows the pump and the disposable cassette inbroken lines.

A disposable cassette generally indicated at 12 is coupled to thedisposable cassette in the pump 10 to receive fluid from the disposablecassette in the pump and pass the fluid to the receiver such as thepatient 14. When the pressure of the fluid in the cassette 12 risesthrough a particular magnitude dependent upon the setting of a knob 64,sensing apparatus generally indicated at 16 becomes operative todiscontinue the operation of the pump. In this way, the pressure of thefluid introduced to the patient is controlled within pre-selectedlimits.

The cassette 12 is shown in some detail in FIGS. 1 and 2. The cassette12 includes a housing 20 having detent means such as tongues 22 disposedexternally on opposite sides of the housing. The housing 20 is shaped todefine conduit means including an inlet line 24, an outlet line 26 and achamber 28 between the inlet and outlet lines. The chamber 28communicates with the inlet line 24 and the outlet line 26.

Resilient means such as a diaphragm 30 is stretched across the chamber28 between opposite sides of the housing 20. An actuatable arm 32 restson the diaphragm and extends upwardly from the diaphragm through anaperture or opening 34 in the housing. In this way, the arm 32 iscaptured by the aperture 34. The arm 32 is disposed in cooperativerelationship with a reinforcement 33 which extends from the diaphragm.The aperture or opening 34 communicates with a passage 35 which has adimension converging towards the relatively narrow dimensions of theaperture or opening 34.

When the sensing apparatus 16 is included in the pump, the arm 32engages resilient means such as a diaphragm 36 on the face of the pump10. The diaphragm 36 may have a construction similar to that of thediaphragm 30. The diaphragm 36 supports an arm 38 which extends upwardlythrough a guide aperture 40 in a housing 42 so as to be guided formovement only in a vertical direction. A constrained spring 43 isdisposed between the housing 42 and a member 45 seated against thediaphragm 36. A flag 44 is carried at the upper end of the arm 38 and ispivotable at one end on a pin 46 as a fulcrum. The flag 44 carries alight source 48.

A pair of bracket members 50 are supported on the housing 42. Springmembers 52 are supported between the housing 42 and the bracket members50. The spring members 52 are provided with spring arms 54 which includedetent means 56 for co-operating with the detent means 22 on thedisposable cassette to hold the cassette in releasable relationship.

A lever arm 60 extends through a threaded aperture in one of the bracketmembers 50. The lever arm 60 receives the knob 64, which is manuallyrotatable to adjust the vertical positioning of the lever arm 60. At itsupper end, the lever arm 60 engages the free end of a spring arm 70, theother end of which is attached to the pump housing 42. A bracket 74 isattached to the housing 42 as by a nut-and-bolt arrangement 76. Thebracket 74 carries a photo sensor 78.

When operative, the pump 10 introduces fluid to the inlet line 24. Thisfluid flows through the chamber 28 and the outlet line 26 to the patient14. The maximum pressure of this fluid is dependent upon the setting ofthe knob 64.

It occasionally happens that the outlet line 26 may become occluded. Atsuch times, the fluid in the outlet line 26 rises into the chamber 28.When this back-up of fluid in the outlet line 26 has occurredsufficiently, the fluid in the chamber presses against the diaphragm 30and forces the diaphragm upwardly. The diaphragm 30 in turn acts uponthe arm 32 to force the arm upwardly.

The diaphragm 36 translates the movement of the arm 32 into acorresponding movement of the arm 38. This produces a correspondingpivotal movement of the flag 44 about the pin 46 as a fulcrum. When theflag 44 has moved through a particular distance dependent upon thesetting of the knob 64, the light source 48 becomes aligned with thephotocell 78. This causes the photocell 78 to become energized andproduces a signal for interrupting the operation of the pump 10.

The particular fluid pressure for energizing the photocell 78 can bemanually adjusted by rotating the knob 64. This causes the lever arm 60to be adjusted vertically in position. The adjustment in the verticalposition of the lever arm 60 in turn produces adjustments in the pivotalposition of the spring arm 70. This in turn produces adjustments in theposition at which the light source 48 becomes level with the photocell78 to energize the photocell.

The apparatus described above has certain important advantages. Itprovides for a flow of fluid from a pump to a patient at controlled andpre-selected pressures dependent upon the setting of the knob 64. If thepressures of the fluid from the pump should increase above suchcontrolled and pre-selected limits, the apparatus instantaneously sensessuch increases in the fluid pressure beyond such controlled and safelimits and causes an output signal to be produced for interrupting theoperation of the pump.

The apparatus described above also has other important advantages. Forexample, it provides a cassette which is easily and releasably coupledto the pump. Furthermore, the flow of fluid from the pump to the patientis only through the cassette. In this way, a different cassette can besubstituted every time that a different patient is to receive theintroduction of fluid or the same patient is to receive a differentfluid. By providing such an arrangement, the pump can be easily adaptedto provide fluid to a patient at relatively low levels of pressurewithout requiring that the pump be cleaned or sterilized after each use.

The apparatus constituting this invention also has other advantages. Inaddition to providing the disposable cassette 12, it provides all of theother elements within the pump housing 42. Furthermore, the diaphragm 36is disposed at the face of the pump. In this way, the diaphragm 36 helpsto seal the pump and also translates the pressure of the fluid on thediaphragm 30 into a corresponding pivotal movement of the flag 44.Although all of the components other than those in the cassette 12 aredisposed in the pump housing 42, it will be appreciated that thesecomponents can also be disposed in a housing which is separate from thepump.

FIGS. 4 and 5 illustrate another embodiment of the invention. In thisembodiment, a cam 100 rotatable on a fulcrum 102 is included. The camincludes a finger 104 for contacting a leaf spring 106, the leaf springbeing attached at one end to a housing 108 by a screw or protuberance110. The cam 100 is shaped to move the finger 104 in a direction towardsthe screw or protruberance 110 in accordance with rotary movements ofthe cam in a clockwise direction and to move the finger in a directionaway from the screw in accordance with rotary movements of the cam in acounter-clockwise direction. The cam 100 is manually rotatable by a knob112.

The spring 106 carries a flag 114 at the end opposite the screw 110. Theflag 114 may interrupt the light from a light source 116 to a sensor 118when it has moved upwardly through a particular distance. The forcerequired to move the flag 114 upwardly through this particular distanceis dependent upon the setting of the cam 100 since this setting controlsthe length of the torque arm between the finger 104 and the flag. Inthis way, the setting of the cam 100 controls the fluid pressure atwhich the light to the sensor 118 becomes interrupted.

Although this application has been disclosed and illustrated withreference to particular applications, the principles involved aresusceptible of numerous other applications which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

.[.I.]. .Iadd.We .Iaddend.claim:
 1. In combination for use with a pumpfor introducing fluid to a receiver and for controlling the pressure ofthe fluid introduced by the pump to the receiver, the pump having detentmeans,an output line for passing the fluid from the pump to thereceiver, a resilient diaphragm connected in the output line forconstraint in accordance with the pressure of the fluid in the line,means movable with the diaphragm for obtaining the production of anoutput indication when the pressure of the fluid in the output line hasreached a particular level, a housing holding the output line, thediaphragm and the movable means, and detent means on the housing forco-operating with the detent means on the pump for releasably holdingthe housing in a particular fixed relationship with the pump.
 2. Thecombination set forth in claim 1 whereinthe housing is constructed tocapture the movable means to provide for a disposition of the movablemeans on the diaphragm and a movement of the movable means with thediaphragm.
 3. The combination set forth in claim 2 whereinthe housingdefines an output line at one end of the housing and defines an inputend at the other end of the housing and defines a chamber between theinput and output lines and wherein the diaphragm is disposed in thechamber.
 4. The combination set forth in claim 1 whereinmeans areadjustable to control the force required to move the movable meansthrough each increment of distance in accordance with variations influid pressure and wherein means are included for providing the outputindication when the movable means has moved through a particulardistance.
 5. The combination set forth in claim 1 whereinmeans areadjustable to control the distance through which the movable means ismoved to obtain an output indication.
 6. The combination set forth inclaim 1 whereinthe diaphragm is disposed in a particular relationship tothe input and output lines in the housing and is stretched across thehousing between the input and output lines.
 7. In combination for usewith a pump for introducing fluid at controlled pressures to a receiverand for providing an output indication when the pressure of the fluidexceeds a particular value, the pump having detent means,conduit meansextending from the pump to the receiver to introduce fluid from the pumpto the receiver, resilient means included in the conduit means forvariable positioning in accordance with variations in the pressure ofthe fluid in the conduit means, actuatable means operatively coupled tothe resilient means for movement with the resilient means to obtain theproduction of the output indication when the resilient means has reacheda particular position, and detent means disposed externally of theconduit means for co-operating with the detent means on the pump to holdthe circuit means in a particular fixed relationship to the pump.
 8. Thecombination set forth in claim 7 whereinmeans are associated with theconduit means for capturing the actuatable means to retain the actuatingmeans for movement with the resilient means.
 9. The combination setforth in claim 7 whereinthe conduit means define input and output linesand a chamber between the input and output lines and wherein in theconduit means support the resilient means in the chamber at a particularposition above the input and output lines.
 10. The combination set forthin claim 9 whereinmeans are associated with the conduit means forcapturing the actuatable means to retain the actuatable means formovement with the resilient means and wherein adjustable means areassociated with the actuatable means to control the variations in fluidpressure required to produce increments in the movement of the resilientmeans and the actuatable means.
 11. The combination set forth in claim 9whereinmeans are associated with the conduit means for capturing theactuatable means to retain the actuating means for movement with theresilient means and wherein adjustable means are associated with theactuatable means to control the variations in the distance of movementof the actuatable means required to obtain the production of the outputindication.
 12. The combination set forth in claim 7 whereintheresilient means constitutes a diaphragm and the actuatable meansconstitutes an arm movable with the diaphragm.
 13. The combination setforth in claim 7 whereinthe resilient means constitutes a diaphragm andthe actuatable means constitutes an arm movable with the diaphragm andthe adjustable means constitutes a manually movable knob and thevariably positioned means constitutes a control lever operativelycoupled to the knob for pivotable movement in accordance with the manualadjustments of the knob.
 14. The combination for controlling the flow offluid to a receiver,a pump, conduit means extending from the pump to thereceiver to introduce fluid from the pump to the receiver, resilientmeans included in the conduit means for variable positioning inaccordance with variations in the pressure of the fluid in the conduitmeans, actuatable means included in the conduit means and operativelycoupled to the resilient means for movements with the resilient means toobtain the production of the output indication when the resilient meanshas reached a particular position, sensing means associated with theactuatable means for sensing when the actuatable means has moved througha particular distance, and detent means disposed in cooperativerelationship on the pump and the conduit means for retaining the conduitmeans in a particular fixed, but removable, relationship to the pump.15. The combination set forth in claim 14 whereinmeans are associatedwith the conduit means for capturing the actuatable means to retain theactuating means for movement with the resilient means.
 16. Thecombination set forth in claim 14 whereinthe sensing means are includedin the pump and wherein the pump also includes resilient meansassociated with the actuatable means in the conduit means for variablepositioning in accordance with the variable positioning of theactuatable means and further includes actuatable means operativelycoupled to the resilient means in the pump for movement with suchresilient means and wherein the sensing means are included in the pumpand are associated with the actuatable means in the pump for sensingwhen such actuatable means has moved through a particular distance. 17.The combination set forth in claim 14 whereinadjustable means areincluded for controlling the fluid pressure at which the sensing meansbecomes operative and means are included in the sensing means forvariable positioning in accordance with the adjustment of the adjustablemeans to control the positioning of the actuatable means at which thesensing means becomes operative.
 18. In combination for controlling theflow of fluid to a receiver,a disposable unit including inlet and outletlines and a chamber between the inlet and outlet lines and a resilientdiaphragm disposed in the chamber between the inlet and outlet lines andresponsive to the pressure of the fluid in the chamber to becomepositioned in accordance with such fluid pressure and including detentmeans, a pump including detent means disposed for cooperation with thedetent means on the disposable unit to hold the disposable unit inremovable relationship, the pump being constructed to pump fluid to theinput line, and means associated with the pump and responsive to thepositioning of the resilient diaphragm for interrupting the operation ofthe pump when the resilient diaphragm has reached a particular position.19. The combination set forth in claim 18 whereinthe means forinterrupting the operation of the pump are included in the pump.
 20. Thecombination set forth in claim 19 whereinthe means for interrupting theoperation of the pump include a resilient diaphragm disposed on the faceof the pump and positionable in accordance with the positioning of thediaphragm in the disposable unit and wherein means are disposed in thepump and are responsive to the positioning of the resilient diaphragm inthe pump for interrupting the operation of the pump when the resilientdiaphragm has reached a particular position.
 21. The combination setforth in claim 18 whereinthe means for interrupting the operation of thepump are separate from the pump.
 22. In combination for controlling theflow of fluid to a receiver,a pump for pumping fluid to the receiver,conduit means for receiving the fluid from the pump and for introducingthe fluid to the receiver, first means associated with the conduit meansand responsive to variations in the pressure of the fluid in the conduitmeans for variable positioning in accordance with such variations influid pressure, and second means responsive to variations in thepositioning of the first means for producing a signal for discontinuingthe operation of the pump when the first means has been displacedthrough a particular distance, the conduit means and the first meansbeing disposed in a cassette and first detent means being provided inthe pump and second detent means being provided in the cassette forcooperation with the detent means on the pump to provide a releasablecoupling between the cassette and the pump, the conduit means includinga housing and inlet and outlet lines, the first means including achamber between the inlet and outlet lines, and means disposed in thechamber and responsive to the pressure of the fluid in the chamber forvariable positioning in accordance with such variations in fluidpressure, the second detent means being disposed on the housing and thefirst detent means include spring arms on the pump for releasablyholding the second detent means.
 23. The combination set forth in claim22 whereinthe second means are included in the pump.
 24. A method ofcontrolling the pressure of a fluid being pumped from a source to apatient, including the following steps:providing a pump for pumping thefluid from the source to the patient and operatively coupling the pumpbetween the source and the patient, passing the pumped fluid through acassette containing a resilient diaphragm constrainable in accordancewith the pressure of the fluid passing through the cassette, convertingthe constraint of the resilient diaphragm to a movement of an outputmember, providing a member adjustable in positioning and cooperativewith the output member to provide an output signal at a position of theoutput member dependent upon the adjustment in the positioning of theadjustable member, and interrupting the operation of the pump upon theproduction of the output signal to maintain within particular limits thepressure introduced to the patient, the constrainable diaphragm in thecassette being coupled to a constrainable diaphragm in the pump toproduce a constraint of the constrainable diaphragm in the pump inaccordance with the constraint of the diaphragm in the cassette and theoutput member being disposed in the pump and being movable in accordancewith the constraint of the diaphragm in the pump and the adjustablemember being disposed in the pump.
 25. In combination for converting apump into a controller for controlling within particular limits thepressure of fluid introduced from a source to a patient,a housing havingan inlet and an outlet for the flow of fluid and having a chamber incommunication with the inlet and the outlet, a resilient diaphragmdisposed in the chamber and constrainable in accordance with thepressure of the fluid in the chamber, a pivotable member, a lightsource, a photocell, means for providing for a variation in the amountof the light passing from the light source to the photocell inaccordance with the variations in the positioning of the resilientmember, and means responsive to a particular change in the passage ofthe light from the source to the photocell for indicating that thepressure of the fluid within the housing has exceeded the particularlimits.
 26. The combination set forth in claim 25, including,detentmeans on the housing for providing for a removable attachment of thehousing to the pump.
 27. In combination for converting a pump into acontroller for controlling within particular limits the pressure offluid introduced from a source to a patient,a housing, detent means onthe housing for releasable attachment to the pump, an inlet into thehousing for receiving the fluid, an outlet from the housing forproviding for the transfer of the fluid from the housing, a chamberwithin the housing in communication within the inlet and the outlet, adiaphragm disposed across the chamber for constraint in accordance withthe pressure of the fluid in the chamber, and an arm disposed incommunication with the diaphragm for transferring the constraint of thediaphragm as a force into the pump.
 28. The combination set forth inclaim 27 whereinthe diaphragm seals the chamber at one end and whereinthe arm extends through the housing for communication with the pump. 29.The combination set forth in claim 27 whereinthe housing is providedwith an opening at one end in communication with the chamber and whereinthe diaphragm is disposed across the opening to seal the chamber fromthe opening and wherein the diaphragm is constrainable in a direction toextend into the opening in accordance with increases in the pressure ofthe fluid in the chamber and wherein the arm is extended through theopening to transfer the constraint of the diaphragm into the pump. 30.The combination set forth in claim 29 whereinthe housing is shaped tofacilitate a manual manipulation of the housing into releasableattachment with the pump and wherein the detent means is disposed on thehousing.
 31. In combination in a disposable unit for operating inconjunction with a pump to control within particular limits the pressureof fluid introduced from a source to a patient,a housing, detent meanson the housing, an inlet for receiving the fluid from the source, anoutlet for passing the fluid to the patient, a resilient diaphragmdisposed across the chamber to close the chamber and to becomeconstrained in accordance with the pressure of fluid in the chamber, areinforcement on the diaphragm at an intermediate position on thediaphragm, an opening disposed in the housing in communication with thereinforcement at the end of the housing opposite the chamber, andforce-transmitting means disposed in cooperative relationship with thereinforcement and extending through the opening to produce a force inthe pump in accordance with the constraint of the diaphragm.
 32. Thecombination set forth in claim 31 whereinthe force-transmitting meansconstitutes an arm disposed in cooperative relationship with thereinforcement and wherein there is a passage in the housing incommunication with the opening and the passage is provided withdimensions converging toward the opening and wherein the arm has atubular portion extending through the passage and the opening totransmit the force on the diaphragm.
 33. The combination set forth inclaim 32 whereinthe reinforcement is hollow and the arm is disposedwithin the hollow interior of the reinforcement.
 34. In combination forcontrolling the pressure of fluid passing from a source to a patient,apump for pumping fluid from the source to the patient, a casingsupported by the pump, there being a socket in the casing, detent meansin the socket, a disposable unit including a housing dimensioned to fitinto the socket and including detent means disposed on the housing tocooperate with the detent means in the socket for removably retainingthe disposable unit in the socket, there being a chamber in the housing,an inlet disposed in the housing and communicating with the chamber toprovide for the introduction of fluid from the source into the chamber,an outlet disposed in the housing and communicating with the chamber toprovide for the passage of fluid from the chamber to the patient, aresilient diaphragm disposed in the chamber to close the chamber andconstrainable in accordance with the pressure of the fluid in thechamber, and means disposed in the pump and responsive to the constraintof the diaphragm for providing an output indication when the pressure ofthe fluid in the chamber has reached a particular limit.
 35. Thecombination set forth in claim 34, including,a knob on the face of thepump casing, the knob being adjustable to different positionsrepresenting individual limits for the pressure of the fluid in thechamber, and the indicating means including means responsive to theadjustments in the positioning of the knob for providing the outputindication when the pressure of the fluid in the chamber has reached theparticular limit represented by the adjustments in the positioning ofthe knob.
 36. In combination for controlling within particular limitsthe pressure of fluid introduced from a source to a patient,a pump forpumping the fluid from the source at a positive pressure, a housinghaving an inlet and an outlet for the flow of fluid and having a chamberin communication with the inlet and the outlet, a resilient diaphragmdisposed in the chamber and constrainable in accordance with thepressure of the fluid in the chamber, means for removably supporting thehousing on the pump, means disposed on the pump for adjustably settingthe particular limits for the pressure of the fluid flowing through thechamber, and means responsive to the constraint of the diaphragm and theadjustable setting of the particular limits for providing an outputindication when the pressure of the fluid in the chamber has reachedsuch particular limits.
 37. The combination set forth in claim 36whereinthe indicating means includes a pivotable member and the memberis coupled to the diaphragm to receive a force in accordance with theconstraint of the diaphragm.
 38. In combination for converting a pumpinto a controller for controlling within particular limits the pressureof fluid introduced from a source to a patient,a pump for directingfluid from the source under pressure, the pump including a casing havinga receptacle, a housing removably disposed within the casing forreceiving the fluid directed from the source by the pump and fordirecting the fluid to the patient, resilient means included within thehousing for constraint in accordance with the pressure of the fluid inthe housing. a knob extending externally from the pump casing andadjustable in position from a position external to the pump casing tocontrol within particular limits the pressure of the fluid within thehousing, and means operatively coupled to the resilient means and theknob for providing an output indication when the resilient means havereceived a particular constraint dependent upon the setting of theadjustable knob.
 39. The combination set forth in claim 38,including,resilient detent means in the casing for removably holding thehousing, and detent means on the housing for cooperation with theresilient detent means in the casing to provide a removable retention ofthe housing by the casing.
 40. The combination set forth in claim39,there being a socket in the casing for receiving the housing, theresilient detent means being disposed in the socket.